119 lines
4.1 KiB
C++
119 lines
4.1 KiB
C++
#pragma once
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#ifndef MESSMER_BLOCKSTORE_IMPLEMENTATIONS_CACHING_CACHE_H_
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#define MESSMER_BLOCKSTORE_IMPLEMENTATIONS_CACHING_CACHE_H_
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#include "CacheEntry.h"
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#include "QueueMap.h"
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#include "PeriodicTask.h"
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#include <memory>
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#include <mutex>
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#include <boost/optional.hpp>
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#include <future>
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#include <messmer/cpp-utils/assert/assert.h>
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namespace blockstore {
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namespace caching {
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template<class Key, class Value>
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class Cache {
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public:
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static constexpr uint32_t MAX_ENTRIES = 1000;
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//TODO Experiment with good values
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static constexpr double PURGE_LIFETIME_SEC = 0.5; //When an entry has this age, it will be purged from the cache
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static constexpr double PURGE_INTERVAL = 0.5; // With this interval, we check for entries to purge
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static constexpr double MAX_LIFETIME_SEC = PURGE_LIFETIME_SEC + PURGE_INTERVAL; // This is the oldest age an entry can reach (given purging works in an ideal world, i.e. with the ideal interval and in zero time)
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Cache();
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virtual ~Cache();
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void push(const Key &key, Value value);
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boost::optional<Value> pop(const Key &key);
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private:
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void _popOldEntriesParallel();
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void _popOldEntries();
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boost::optional<Value> _popOldEntry();
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static void _destructElementsInParallel(std::vector<CacheEntry<Key, Value>> *list);
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mutable std::mutex _mutex;
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QueueMap<Key, CacheEntry<Key, Value>> _cachedBlocks;
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std::unique_ptr<PeriodicTask> _timeoutFlusher;
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};
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template<class Key, class Value> constexpr uint32_t Cache<Key, Value>::MAX_ENTRIES;
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template<class Key, class Value> constexpr double Cache<Key, Value>::PURGE_LIFETIME_SEC;
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template<class Key, class Value> constexpr double Cache<Key, Value>::PURGE_INTERVAL;
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template<class Key, class Value> constexpr double Cache<Key, Value>::MAX_LIFETIME_SEC;
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template<class Key, class Value>
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Cache<Key, Value>::Cache(): _cachedBlocks(), _timeoutFlusher(nullptr) {
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//Don't initialize timeoutFlusher in the initializer list,
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//because it then might already call Cache::popOldEntries() before Cache is done constructing.
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_timeoutFlusher = std::make_unique<PeriodicTask>(std::bind(&Cache::_popOldEntriesParallel, this), PURGE_INTERVAL);
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}
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template<class Key, class Value>
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Cache<Key, Value>::~Cache() {
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}
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template<class Key, class Value>
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boost::optional<Value> Cache<Key, Value>::pop(const Key &key) {
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std::lock_guard<std::mutex> lock(_mutex);
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auto found = _cachedBlocks.pop(key);
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if (!found) {
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return boost::none;
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}
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return found->releaseValue();
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}
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template<class Key, class Value>
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void Cache<Key, Value>::push(const Key &key, Value value) {
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std::lock_guard<std::mutex> lock(_mutex);
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ASSERT(_cachedBlocks.size() <= MAX_ENTRIES, "Cache too full");
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if (_cachedBlocks.size() == MAX_ENTRIES) {
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_cachedBlocks.pop();
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ASSERT(_cachedBlocks.size() == MAX_ENTRIES-1, "Removing entry from cache didn't work");
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}
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_cachedBlocks.push(key, CacheEntry<Key, Value>(std::move(value)));
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}
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template<class Key, class Value>
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void Cache<Key, Value>::_popOldEntriesParallel() {
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unsigned int numThreads = std::max(1u, std::thread::hardware_concurrency());
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std::vector<std::future<void>> waitHandles;
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for (unsigned int i = 0; i < numThreads; ++i) {
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waitHandles.push_back(std::async(std::launch::async, [this] {
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_popOldEntries();
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}));
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}
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for (auto & waitHandle : waitHandles) {
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waitHandle.wait();
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}
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};
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template<class Key, class Value>
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void Cache<Key, Value>::_popOldEntries() {
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// This function can be called in parallel by multiple threads and will then cause the Value destructors
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// to be called in parallel. The call to _popOldEntry() is synchronized to avoid race conditions,
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// but the Value destructor is called in this function which is not synchronized.
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boost::optional<Value> oldEntry = _popOldEntry();
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while (oldEntry != boost::none) {
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oldEntry = _popOldEntry();
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}
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}
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template<class Key, class Value>
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boost::optional<Value> Cache<Key, Value>::_popOldEntry() {
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std::lock_guard<std::mutex> lock(_mutex);
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if (_cachedBlocks.size() > 0 && _cachedBlocks.peek()->ageSeconds() > PURGE_LIFETIME_SEC) {
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return _cachedBlocks.pop()->releaseValue();
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} else {
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return boost::none;
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}
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};
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}
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}
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#endif
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